DENVER — A United Nations-based drug agency urged the United States government on Tuesday to challenge the legalization of marijuana for recreational use in Colorado and Washington, saying the state laws violate international drug treaties.

The International Narcotics Control Board made its appeal in an annual drug report. It called on Washington, D.C., to act to “ensure full compliance with the international drug control treaties on its entire territory.”

U.S. Attorney General Eric Holder said last week that he was in the last stages of reviewing the Colorado and Washington state laws. Holder said he was examining policy options and international implications of the issue. Marijuana is illegal under federal law.

The federal government could sue the states over legalization or decide not to mount a court challenge. Washington and Colorado became the first states to pass laws legalizing the recreational use of marijuana in last fall’s elections.

“The entire international system is based on countries respecting the rules, and there’s a broad fabric of international treaties that are part and parcel to that,” said David Johnson, the U.S. delegate to the Vienna-based board.

The control board is the independent monitoring body for the implementation of United Nations drug control conventions. Its head, Raymond Yans, also called on Holder to challenge the laws soon after voters in both states approved them in November.

The director of the Open Society Foundations’ Global Drug Policy Program, Kasia Malinowska-Sempruch, blamed repressive drug laws for millions of arrests and called on the United Nations General Assembly to reconsider its approach when it holds a special session on drugs in 2016.

The U.N. report also cited prescription drug abuse as a continuing problem as well as the emergence of so-called designer drugs that are engineered to fall out of the scope of existing drug controls.